Automatic toner concentrate detector



Jam 6 1970 s. A. GAwRoN AUTOMATIC TONER CONCENTRATE DETECTOR OriginalFiled June 14, 1967 2 Sheets-Sheet 1 Jan. 6, 1970 s. A. GAwRoN 3,487,978

AUTOMATIC TONER CONCENTRATE DETECTOR Original Filed June 14, 1967 2Sheets-Sheet 2 United States Patent O Int. Cl. G01f 11/00 U.S. Cl. 222-11 Claim ABSTRACT F THE DISCLOSURE A rotating reflective disc locateddirectly in a developer mix containing toner is electrically biased sothat it will attract toner from the mix. The amount of toner attractedto the surface of the disc is a function of the concentration of tonerin the mix. A light beam is directed to reflect off the surface onto aphotoelectric unit, with the intensity of the light striking the unitbeing controlled by the amount of toner on the surface. Thephotoelectric unit and source of light are mounted in a protectivehousing in order to render them free of toner dust. The unit iscalibrated to signal a dispensing apparatus to operate when theintensity of the reflected light indicates a less than optimum tonerconcentration.

This application is a division of copending application, Ser. No.646,056, filed June 14, 1967, now Patent No. 3,399,652.

BACKGROUND OF THE INVENTION This invention relates to an apparatus whichmonitors and controls the feeding of toller to a mass of developer mixin accordance with the concentration of toner in said mix. Moreparticularly, this invention relates to `an apparatus for continuouslymeasuring the concentration of toner in the developer mix by opticallysensing the amount of toner that is triboelectrically attracted to asampling medium. In accordance with the well known electrostaticprinting process, a surface bearing a latent electrostatic image isdeveloped by selectively applying a developer mix comprising toner and acarrier medium to the image. With repeated use of the mix toner isgradually consumed until there is no longer a suicient concent1-ation oftoner in the mix to develop high quality, dense images.

The prior art systems of monitoring toner concentration follow twogeneral schemes of measurement, electrical and optical. Electricalsystems depend on measuring the changes in resistance of the mix as thehigh resistivity toner component varies in relation to the conductivecarrier component, and the optical systems depend on measuring thedensity of a calibrated toner test pattern. In the latter system thetest pattern is established in accordance wih the concentration of tonerin the mix provinding a graduated visible scale correlated to the tonerconcentration as determined yby an optical sensing device.

The prior art systems are somewhat deficient in that variations in thetoner formulation in the case of the electrical systems require frequentcalibration checks to account for any changes in resistance of thethermoplastic resin. Optical systems are confronted with theinterference due to the airborne particles falling on the opticalsensing components which result in false readings and in general requirefrequent cleaning maintenance of all the components in order to be surethat no erroneous measurements occur.

3,487,978 Patented Jan. 6, 1970 ice lt is the general object of thisinvention to provide an improved automatic toner feed control devicethat is accurate, reliable and free of frequent cleaning maintenance.

It is a further object of this invention to provide an automatic tonerfeed control that monitors the concentration directly at the point ofaddition of the toner so that there is little time-lag between thegeneration of the monitoring signal and the activation of the dispensingdevice in either starting or stopping.

It is still another object of this invention to provide an automatictoner feed control in which the toner sampling device is self-cleaning.

It is still another object of this invention to provide an automatictoner feed control in which optical components used to measure theamount of toner deposition are protected against the accumulation of thetoner from out the optical path.

It is a specific object of this invention to provide an automatic tonerfeed control `which is capable of operating under changing temperatureconditions. A related object is to provide a temperature responsivecontrol operatively associated with the photoelectric instru ments whichcompensate for fluctuation of the temperature.

It is still another specific object of this invention to provide a tonerfeed control device which is particularly well adapted to be used inconjunction with conventional magnetic brush developing assemblies.

The present invention comprises a conductive probe having a reflectiveor transparent light transmitting specular surface, a reflective surfacebeing preferred, means for bringing the probe and mix into Contact tocollect a sample of toner on the specular surface, means forphotoelectically measuring the amount of toner on the surface, anddispensing means for adding toner to the mix in accordance with theamount of toner attracted to and retained on the probe. The term lighttransmitting as used herein refers either to the light reflectiveproperty of the probe or its transparent property. The probe isconnected to a DC potential imparting to the specular surface atoner-attracting electrostatic charge which is uniformly distributedover the surface to establish an electrical field of uniform intensity.The range of voltage to be applied can vary widely depending on thenature of the mix formulation and, in particular, the type of resintoner employed. In a typical magnetic brush arrangement where theresistivity of the toner is in the range of from 1010-1012 ohmcentimeters and the carrier is iron, the applied voltage can range from25-200 volts, preferably in the range of from 40-60 volts. It has beenfound that, if the biasing potential applied to the probe is Within therange of from about 40-60 volts DC, the probe is selfcleaning. It isrealized that this device can be biased at higher levels, but as thebiasing potential increases, the toner on the disc becomes moredifficult to remove and reversing the polarity of the biasing potentialor other measures must be taken to clean the probe. The electrical eldattracts toner from the mix and deposits the micron-size particles overthe probe surface in a uniform manner to provide a horogeneous tonerVformation thereon. It will be appreciated that the action of the probeis to simulate the'developing step of the apparatus so that there isclose correlation between the monitoring device and the actual imagingprocess that takes place in a copying machine.

The preferred construction of the probe is that of a rotatable member,such as, for example, a disc. In accordance with the preferredembodiment of this invention, a rotating disc formed into a plurality ofradially extending iin portions is partially immersed in a mass ofdeveloper mix. It is preferred that the finned disc be located in themix directly where the toneris dispensed. As the disc rotates, toner isattracted from the mass onto the surface of the fins and withdrawn to aviewing zone where the change in reflectivity on each of the fins, dueto the attraction of the toner, is measured. Since the disc isconductive, preferably formed of metal, the charge is uniformlydistributed over the n surface. It has been found that, for optimumresults, the n surface should provide a greater area than the viewingarea of the photocell. However, it is understood that the continuousrotation of the disc provides continuous sampling of the mix which ismonitored by the photocell and provides a system which, in effect,integrates a large number of lsamplings so as to provide a fairlyaccurate control.

This device has been found to be particularly well adapted for use withconventional magnetic brush developing assemblies, although it iscontemplated that this device is equally Well adapted for use with othertypes of developing apparatus, such as cascade developers.

The optical measuring means include a light source, a photodiode whichfunctions as a light-responsive switch in this control, and atemperature control device which is operatively associated with thephotodiode to compensate for changing temperature conditions whichaffect the response characteristics of the photodiode.

To avoid deposition of the airborne toner on the light source, it isenclosed in a protective housing having a light access opening. Thehousing is formed of materials which 'are triboelectrically similar tothe triboelectric characteristic of the toner. Housings formed ofplastics, such as acrylic resins or polyvinyl acetate resins, tend to betribolectrically positive and, hence, they will repel the positivelycharged toner. However, it should be understood that other materials ofconstruction may be used which are conductive in which case an externalfield may be applied to the housing to create the equivalent effect ofusing triboelectrically oriented plastic materials.

To further reduce the likelihood of toner deposition on the sensingdevice, the housing construction provides for a pair of light conductingchannels which converge at a common opening in the front of the housingjuxtaposed the face of the fin portions. The light source and thephotodiode are each received in one of the channels at points remotefrom the common opening. The common opening at which the channelsconverge serves as an exit way for the light rays which are directedonto the ns from the light source, and at the same time act as an entryway to -the other channel in which is mounted the photodiode for,sensing the lightrays reflected fromthe n surface. Accordingly, thelight source is mounted at the head of one of the channels and thephotocell is `locatedat the end'of the second channel, Thisitype of anarrangement serves to protect the emission source and the' sensingelement from the interfering effects of toner dust which may tend toaccumulate thereon.

BRIEF DESCRIPTIONv E vDRAWING Other objects and features of thisinvention will become apparent from the; following description takenvin' connection with the accompanying drawingsY in which:

FIGURE 1 is a perspective view of a portion of a con- `ventonal magneticbrush developing'apparatus showing DESCRIPTION 0E PREFERRED EMBODIMENTAccording to FIGURES 1 and 2, there is shown a magnetic brush assembly,indicated generally as 10, and the toner feed control of this invention,indicated generally 'The assembly 10 is a conventional magnetic brushassembly such as disclosed in detail in U.S. Patent No. 3,- 003,462,which includes `a rotatably mounted cylinder 14, (FIGURE 2), havingmagnetic pole pieces 1 6 disposed .within and"v along the longitudinalaxis rof the cylinder,

"and a pair of augers 18 and 20 which, working in con- "ce'rt, serve'tocirculate the vmix 22 laterally through the trough 24.v As se'en fromFIGURE 2,'the auger 18 isY ro- `tateclin ac'ounterclockwise direction4moving a portion 'of' the mix'22 from'the trough 24 to the assembly 10.Simultaneously/g the auger '20 'is being rotated in a clocks'e directionto return the mixl from th'e'assembly 10 vto afthe "'trough 2(4'for`replenishment with fresh toner. The .'vc'ylin'der 14 is rotated inacou'nterclockwise direction, "and aslit rotates,v it' collects on itsouter surface developer mix Being fed by the auger 18. Under theinfluence of lt'liel'magnetic *field produced bythe magnetic pole piece16, the magentic mix 22 is formed in the configuration of a magneticbrush 26 on the periphery/'of'r the cylinder '14.By vbringing a sheetbearing a latent electrostatic image intotangentialcontact with/thebrush 26, the image lis Iselectively developed. Y L.

l As the cylinder 14 continues to rotate, Iand the brush"'26-whichiscarried thereon is moved'beyond the influence fofthemagnet'icfux lield established by the pole pieces 4 16. The mix-is'the'nvreleased from the surface-'of the 'cylinder 14 and-falls backinto the `main body' of the mix being circulated by the auger 20. Thetoner concentration vmonitoring assembly," identified generally as 28,is disposed in` the`tr`ough424 which serves as-the terminal point Aforthe usedlmix before it is recirculated by the auger `18.

It is at this station that fresh toner 30 is dispensed into `the trough2'4'fror'n 'a dispensinghopper- 32. A detailed lchrome-plating orsimilar' surface treatment in order to provide a specularly reflectivesurface. The disc member 34 "is mounted on a shaft 40 coupled to a drivemotor 42,-It will be observed that the disc member 34 is situatedbetween the 'angers 18 and 20 rotating in a plane normal to the lplanepassing through the axes of rotation of the respective augers. The disc34 is partially immersed in the developer mix 22 Where it is exposed toa representative sampling ofthe mixture to be analyzed Vfor the con-"Ic'entration of toner therein. vImmediately adjacent the specularlyreflective'face -portion 38 of the disc member .'34 is alight'reflect'ance sensing unit 44 encased in ardust- :protectivehousing 46 attached by means of a bracket 48 to the trough 24. Thehousing 46 construction provides for' a pair of converging channels 50and 52 (FIGURE 3) which converge to a common opening 54 atthe frontportion of the housing juxtaposed thedisc 34 immediaterthe face portions38. Itwwill hefapparent that vthe'rotation of the discmember 34 causesIa good deal of toner powder in the mix to become airborne, particularlyinthe; immediate vicinity 'of the sensing unit 44.

At the head of channel 52 is a light source '56 operating inconjunction'with ailens element 58y directing the light through the opening 54which serves as an exit Way for the light rays to be impinged on theface portions 38 of the-tins 36.=The..light Irays impinge upon the faceportion 38 at an angle of incidence and are reflectedtherefrom into theopening -54 `vat any'angle of reection from the surface which is equaltothe angle of incidencefromthe light source 56. The light proceeds into`the channel 52 .at'theend of Which'is alight-responsive photodiode 60and afocusing lens 62. This photodiode 60 may be a conventionalphotocell or a silicon-duodiode. The vangular relationship of thechannels is such as to conform to the angle of incidence and the angleof reflection of the light rays impinging and being reflected from theface surface 38 of the fins 36. It will be appreciated that the locationof the light source and the photocell inside their respective channelsat a location remote from the opening 54 protects these elements frombecoming coated with the toner dust. In this manner the all-importanttransmission and reception of the light rays vital to the operation ofthe sensing unit is not impaired.

It has 'been found desirable for the material of construction of thehousing 46 to have triboelectric characteristics the same or similar tothe toner. The similarity of triboelectric characteristics prevents theattraction of toner to the housing. A wide variety of plastic materialsmay be used, such as acrylic ester polymers and poly-Vinyl acetates,which have been found to be particularly suitable for the application.lt is to be understood that, while the preferred materials ofconstruction are plastic, other materials of construction may be used,such as metals, which may be electrically blased by an external sourcein order to create the necessary charge relationship to the tonerparticles and thereby obtain the equivalent result as using atriboelectrically oriented plastic material.

In order to achieve consistant and invariant measurement, thelight-responsive photodiode 60 includes a temperature-sensing element 66such as a thermistor located adjacent the photodiode 60. An increase intemperature of the photodiode 60 environment will affect its responsebecause of its inherent characteristic to undergo a decrease inresistance. Accordingly, an increase in temperature Would result in anerroneous output lowering the resistance beyond what is attributable toreflected energy which is the significant energy toY be measured. Thethermistor control 66 serves to shunt off a proportional amount of theoutput current due to a change in the operating temperature in theenvironment of the diode 60 so that the control portion of the mechanismreceives a signal primarily based on the quantity of radiation beingreflected from the specularly reflective face portions 38.

To further reduce the possibility of occluding the photodiode 60 or thelight source 56 with toner particles, the housing 46 is mounted at anoblique angle with the opening 54 at a lower elevation than thephotodiode or the light source. To accommodate this angular position ofthe housing 46, the face portions 38 of the fins 36 may be formed at anangle so that the light rays from the light source are directed along aline normal to the face portion. This technique of positioning thehousing 46 in relation to the disc 34 keeps out the larger particleswhich are heavy enough to be prevented by the gravitational forces frommoving up into the respective channels 50 and 52.

Referring to FIGURE 4, there is shown the control circuit 68 connectedby feed lines to a 11S-volt AC power supply controlled by a double-pull,single-throw switch 72. The control circuit 68 includes the drive motor42 which drives the disc 34., a vibrating coil 74 for vibrating,

the hopper dispenser 32 and the toner sampling circuit and monitoringcircuit, identified generally as 76 and 78, respectively. The constantvoltage transformer 82 is connected across the 11S-volt line whichpowers the primary winding 83 of the transformer 82. The toner samplingand toner monitoring circuits are connected to the secondary windings85, 86 and 88 of the transformer 82.

The light source 56 is connected across the winding 8S in series with al0 ohm variable resistor 87 used to adjust the intensity of the lightsource in accordance with the characteristics of the photodiode 60.

A biasing potential of about 50 volts DC is applied to the disc 34 fromthe winding 86 which feeds the input to a full-wave rectifier 92 whichis, in turn, connected through resistors 94 and 96 arranged in parallelconnection. The resistors 94 and 96 are rated at 820 kiloohms. When thetoner employed is positively charged, the disc is connected as shown sothat a negative charge is applied thereto. When the toner employed is ofa negative polarity,

the connections between the disc 34 and the rectifier 92 are reversed sothat the disc is charged to a positive polarity.

Winding 88 supplies power to the toner monitoring circuit 78. Thewinding 88 is connected to the input terminals of a full-wave rectifier98. Across the output terminals of the rectifier 98 is connected afilter network consisting of a pair of 50 microfarad condensors 100 and104 across a 33-ohm resistor 102. The output of the filter network isconnected to the input line of the photodiode 60. The negative outputterminal of the rectifier 98 leads to the thermistor 66. Variableresistor 108 is in series connection with the variable resistor 110leading to the output side of photodiode 60. As a result of the constantillumination of the photodiode 60 and its proximate location to thelight source 56 (FIGURE 3), the temperature of the photodiode graduallyincreases with use. Since the only variable factor in the monitoringsystem should be the amount of toner deposited on the fins 36, thetemperature control device, such as the thermistor 66, serves to drawoff a proportional amount of the output of the diode attributable to theincreased heat of the system.

As the environment heats up, the photodiode 60 increases in thetemperature causing the drop in resistance, and hence, resulting in agreater current output to the transistors 114 and 116 which function asa high-gain amplifier control. In order to control the current outputcaused by heat, the thermistor 66, in close proximity to the photodiode60, also undergoes a decrease in resistance and, hence, serves to shuntthat portion of the heatproduced current around the transistor network.The resistors 108 and 110 serve to modify the response characteristicsof the thermistor so that it is compatible withy the diodecharacteristics at the given temperature of operation so that only thatportion of the output due to heat is shunted off.

The diode 60 is at its high impedance level when the light being cast onit is at a low intensity level. Since the fin portions 36 are spacedapart as the disc rotates, it produces a discontinuous refiected lightpattern. To negate the effect of this intermittent illumination of thephotodiode, there is provided a condenser 112 to even out the outputsignal of the photodiode 60.

When the output signal from the photodiode 60 reaches a predeterminedlevel, it will fire the transistor 114 which will permit current to fiowto the base of transistor 116- Which, in turn, at the predeterminedlevel will also fire causing current to flow through resistor 120 to thepredriver transistor .122. The firing level of the pre-driver transistor122 is controlled by the variable resistor 124.A

Upon reaching the firing level 0f the transistor 122, it

supplies current to the lbase of the output driver transistor 126 whichenergizes the coil of the main relay 130A pulling in its contacts 13'2energizing the vibrating solenoid 74 to dispense the toner into thetrough 24. The 20-microfarad condenser 134 in parallel relation to thecoil 130 protects the driver transistor 126 against lock when the coilis de-energized. The resistors 136, 138 and are current limitingresistors; resistor 144 (l0 kiloohms) sets the level of voltage responsefor transistor 122 with the unsaturated range of the high gain amplifiercircuit of transistors 114 and 116. Resistor 142 assures that the baseof transistor 122 does not reach ground potential.

To place the apparatus in operation, the switch 72 is closed energizingthe drive motor 42 and the primary coil 83 of the constant voltagetransformer 82. The disc member 34 begins to rotate at a speed not inexcess of 50 r.p.m. It will be appreciated that the particular speed atwhich the disc 34 is rotated may -be varied over a wide range, the onlylimitation being that its speed =be adjusted so as not to stir up thedeveloper mix to the point where it Ibegins throwing out the particlesfrom the trough 24. Insulating spacers 136 and 138 (FIGURE 1) areprovided between the motor and the trough wall, and for the shaft 40, inorder to electrically insulate the disc 34 from ground so that the discis electrically oating. AS the disc member 34 moves through thedeveloper miX 22, toner is attracted to the ns, and in particular to thespecularly reflective face portions 38 in accordance with theconcentration of toner on the mix. It will be appreciated that the discmember 34, being of a different material than the developer mix, willgenerate triboelectric forces such that the powder will be attracted tothe specularly reflective surface. However, it is perferred that abiased charge be applied to the disc as provided -by the secondarywinding 86 through the rectier 92. The voltage applied is in the rangeof from 40-60 volts causing the attraction of the electroscopic powder.

Simultaneously, the light source 56 is energized causing radiation inthe visible range f the spectrum to be directed on the face portions 38of which has been attracted a certain amount of toner. The intensity ofreected light from the specularly reective surface 38 may be correlatedto the toner concentration in the mix, since the amount which isattracted to the surface is directly dependent on the concentrationpresent in the mix. By adjusting the variable resistor 110, the outputcurrent level at which the transistor 114 is to be red may be preset.The variable resistor 110 operating in conjunction with the diode 60determines the current level at which the transistor 114 will re causingcurrent to flow to the base of transistor 116 leading to the pre-drivertransistor 122. In the circumstance that the current level isinsufficient to fire the transistor 114, it returns to the input side ofthe photo diode through the resistor (1.5 kiloohms) 138. The high-gainamplication achieved through the transistors 114 and 116 directs thesignal to the pre-driver transistor 122 controlled yby the variableresistor (l5 kiloohms) 124.

When the pre-driver transistor 122 res, it permits the passage ofcurrent through resistor kiloohms) 127 to the base of the transistor1'26 which then energizes the relay 130 which pulls in its contacts 132energizing the vibrator mechanism 74 of the hopper 32, which thenybegins the vibrator mechanism 74 of the hopper 32, which then Ibeginsthe dispensing of fresh toner into the trough 24.

The calibration of the device will depend on the nature of the material,but in general the operator will determine the concentration in the mixwhich results in the optimum quality reproduction, and itis thisconcentration for which the toner sampling circuit 7-6 and the tonermonitoring circuit 78 are adjusted to maintain.

As the fresh toner is dispensed from the hopper 32, it falls directlyinto the trough 24 and there is intermixed with the existing developermix by the augers A18 and 20, and the disc member 34 immediately samplesthe replenished developer mix which in turn is immediately monitored bythe toner monitoring circuit 78 so that an instantaneous reading isobtained without any undue delay or lag between the addition ofv tonerand the readout,

Although the present invention has been described with reference to anillustrative embodiment thereof, it should be understood that numerousother embodiments and modifications can be devised `by those skilled inthe art that would fail within the spirit and scope of this invention.

What is claimed is: l

1. The method for automatically controlling the concentration of tonerin a developer mix to a predetermined level as measured by usingphotoelectric detection means and a probe in conjunction with tonerdispensing means preset to dispense toner responsive to said detectingmeans upon detecting an amount of toner less than said predeterminedconcentration comprising the steps of (l) inserting the probe into thedeveloper mix for attracting a first quantity of toner thereon dependenton the concentration of toner in the mix;

(2) withdrawing said probe from the developer mix to a viewing position;

(3) irradiating the probe with a beam of radiant energy;

(4) detecting the amount of radiant energy transmitted from the probeand generating a signal correlated to the toner concentration in themix;

(5) dispensing fresh toner into said mix when said signal level is belowthat set for the predetermined concentration level;

(6) 'reinserting said probe into the mass whereup said iirst quantity isreleased an a second quality of toner adheres;

(7) repeating steps 2-5 until the signal level correlates to thepredetermined concentration level.

References Cited UNITED STATES PATENTS y3,224,649 12/1965 Gum@ zzz- 1993,300,091 l/1967 Wondrak et al. 222-76 3,419,188 12/1968 Mrchen 2224-76XR ROBERT B. REEVES, Primary Examiner U.s. c1. X.R. 222-52 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,487,978 January 61970 Stanley A. Gawron It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected asshown below:

Column 2, line 63, "horogeneous" should read homo eneous Column 4, line37, "3,224,468" should read 3,224, 49 line 73, "This" should read TheColumn 7, lines 4l and 4 cancel "the Vibrator mechanism 74 of the hopper32, which then begins". Column 8, line l2 "fail" should read fall line"thereon" should read therein line 35 "whereup" should r` whereupon line36 "an" should read and same line "quality" should read quantity Signedand sealed this 3rd day of November 1970.

(SEAL) Attest: A

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

